Yep the same thing happened to my 99. The ODO would reset and all the gauges peg out at the other position. Exp...the speedo would go to 155 and the TAC would go to 7,000. It is the Gauge cluster going bad.It will start doing it all the time not just when its cold. The dealership will fix it.

Will they take care of it even if it's not under warranty, since there is a TSB?

Not likely. The only time that you have repairs done out of warranty at the Dealers expense is under a safety recall. Other than that, your SOL Dude.

A TSB is information that is made available to the Technicians by the Manufacturer. TSB info is not intended for our eyes. Just because GM is aware of a problem and puts it on the TSB list, doesn't mean that it will get repaired at GM's expense outside of your original warranty period.